“The Brexit date may be 29th March, but it is only may be. Brexit is not inevitable. It can and must be stopped,” Mr Cable told party activists in Brighton.

In a bid to put pressure on the Labour front bench over its refusal to support the People’s Vote campaign for a referendum to approve the Brexit deal, Mr Cable appealed to Labour members gathering in Liverpool in four days’ time.

“Next week hundreds, thousands, of Labour members and MPs will demand he changes course and backs a public vote on the final deal.

“If Jeremy Corbyn will not say “I will support a People’s Vote and I will fight Brexit”, Labour members should wave him goodbye.”

Mr Cable also mounted a stinging attack on Boris Johnson, describing him as the “Chancer in Chief” and comparing him to Donald Trump.

He said Conservative Brexiteers were either ‘true believers’ who believe any economic cost is worth the “erotic spasm” of leaving the EU, ‘conscripts’ like Theresa May and Philip Hammond, who have “signed up to Brexit out of a misplaced sense of duty”, and ‘chancers’ like Mr Johnson and Michael Gove.

“He and Michael Gove embraced Brexit after tossing a coin, or making a cold calculation about the quickest route to the top of the Conservative Party,” Mr Cable said.

“As Boris discovered in the last Tory leadership election, Michael Gove is the ideal man for a penalty shootout – right to the last moment you never know which way he will go.”

He added: “Boris Johnson is a real danger to Britain,” Mr Cable said. “He doesn’t just resemble Trump – large, loud and blonde – he behaves more like him by the day.”

He appealed to moderate MPs in both parties, urging them to help the Lib Dems build a new centrist force in British politics.

“Much now depends on the courage of mainstream MPs in the Labour and Conservative parties,” Mr Cable said. “They are losing control and if they can’t stop the rot, they should leave.”

He defended proposals to open up the Lib Dems to non-paying ‘supporters’ who could vote in leadership elections and choose a successor to Mr Cable from outside the party.

“There may be a temptation to be what our colleagues in Scotland might call the ‘wee frees’ of British politics, sniffing suspiciously at newcomers and outsiders, who lack doctrinal purity,” Mr Cable said.